Customized acetabular cup positioning guide and method of generating and employing such a guide

ABSTRACT

Implementations described and claimed herein provide an arthroplasty system and methods for positioning an acetabular cup implant. In one implementation, the system includes a shape-match hip guide having a patient specific mating region that is a negative of the surface contour of the inside surface of the patient&#39;s acetabular cup, and a directional rod that extends generally along the axis of the patient&#39;s femoral head and femoral neck. They system can additionally include an outrigger or silo device to aid in the alignment of surgical tools for preparing and implanting of the prosthetic acetabular cup in the patient&#39;s acetabular cup. Related methods are also disclosed herein for generating a shape-match guide and implanting an acetabular cup with the guide.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 13/960,498 filed Aug. 6, 2013, which application claimspriority under 35 U.S.C. § 119 to U.S. provisional patent application61/794,662, which was filed Mar. 15, 2013, entitled “ACETABULAR CUPPOSITIONING.” Both applications are hereby incorporated by reference intheir entireties into the present application.

FIELD OF THE INVENTION

Aspects of the presently disclosed technology relate to medicalapparatuses, systems, and methods. More specifically, the presentlydisclosed technology relates to a customized acetabular cup positioningguide and surgical systems and methods for generating and employing theguide and implanting an acetabular cup with the guide.

BACKGROUND OF THE INVENTION

Over time and through repeated use, bones and joints can become damagedor worn. For example, repetitive strain on bones and joints (e.g.,through athletic activity), traumatic events, and certain diseases(e.g., osteoarthritis) can cause cartilage in joint areas, whichnormally provides a cushioning effect, to wear down. When the cartilagewears down, fluid can accumulate in the joint areas, resulting in pain,stiffness, and decreased mobility.

Arthroplasty procedures can be used to repair damaged joints. During atypical arthroplasty procedure, an arthritic or otherwise dysfunctionaljoint can be remodeled or realigned or an implant can be implanted intothe damaged region. Arthroplasty procedures may take place in any of anumber of different regions of the body, such as a knee, a hip, ashoulder, or an elbow.

One type of arthroplasty procedure is a total hip arthroplasty (“THA”)procedure, which consists of replacing both the acetabulum, also knownas acetabular cup, and the femoral head with prosthetic implants.Another type of arthroplasty procedure is a hemi or half hipreplacement, which consists of replacing just the femoral head with aprosthetic implant. The hip joint may have been damaged by, for example,arthritis (e.g., severe osteoarthritis or degenerative arthritis),trauma, or a rare destructive joint disease. Typically, a THA procedureis conducted to relieve pain due to osteoarthritis or to remedy severejoint damage as part of hip fracture treatment.

The hip is one of the largest joints in the human body. The hip consistsof a ball and socket, wherein the socket is formed by the acetabulum,which is part of the pelvis bone. The ball, in the ball and socketsystem, is the femoral head, which is at the proximal end of the femur.The surfaces of the ball and socket are covered with articularcartilage, a smooth tissue that cushions the ends of the bones andenables femoral head and the acetabulum to move easily. A thin tissuecalled synovial membrane surrounds the hip joint. In an otherwisehealthy hip joint, this membrane makes a small amount of fluid thatlubricates the cartilage and eliminates almost all friction during hipmovement. Bands of ligaments connect the ball to the socket and providestability to the joint.

During a THA procedure, a damaged portion of bone in the femoral headmay be removed and replaced with a femoral prosthesis or implant, and adamaged portion of the bone and cartilage in the acetabulum may beremoved by reaming, scraping, cleaning or otherwise preparing of theacetabular surface to receive an implanted prosthesis, such as aprosthetic acetabular cup. After the damaged portion of the femoral headis removed, the femoral prosthesis, which includes a stem, may becemented or simply press fitted into the patient's femur. Similarly, theacetabular cup may be screwed, pinned, cemented, or otherwise coupled tothe patient's acetabulum. The acetabular cup can additionally include anosseointegrated surface to enhance the fusion of the bone to theimplant. The interface between the acetabular cup and the femoralprosthesis is the ball and socket joint, or the articular interface. Thespecifications for the articular interface (e.g., make, model, size,material) vary depending on the patient's bony anatomy, health, activitylevel, and associated risks involved with the procedure.

Implants that are implanted into a damaged region may provide supportand structure to the damaged region and may help to restore the damagedregion, thereby enhancing its functionality. Prior to implantation of animplant in a damaged region, the damaged region is prepared to receivethe implant. For example, in a hip arthroplasty procedure, one or moreof the bones in the hip area, such as the femur and/or the acetabulum,may be treated (e.g., cut, drilled, reamed, and/or resurfaced) toprovide one or more surfaces that can align with the implant and therebyaccommodate the implant.

Accuracy in implant alignment is an important factor to the success of aTHA procedure. Preparing a patient's acetabulum for implanting of aprosthetic acetabular cup can be challenging because of the uniquecontouring shape of the patient's acetabulum, and because the pelvicbone does not easily lend itself to resections, as in an arthroplastyprocedure involving implants to the femur or tibia. These factorsunderscore the importance of properly preparing the acetabulum prior toa THA procedure and properly aligning the acetabular cup to theacetabulum. A one to two millimeter translational misalignment mayresult in imbalanced ligaments and thus may significantly affect theoutcome of the procedure. For example, implant misalignment may resultin intolerable post-surgery pain and also may prevent the patient fromhaving stable leg flexion. In particular, the patient's joint may not berestored to its natural alignment with respect to the knee and anklecenters, which can result in pain and difficulty in adjustment to thenew alignment.

To achieve accurate implant alignment, prior to treating (e.g., cut,drilled, reamed, and/or resurfaced) any regions of a bone, it isimportant to correctly determine the location at which the treatmentwill take place and how the treatment will be oriented. In some methods,an arthroplasty guide may be used to position and orient a resection,sawing, or implantation instrument, such as a cutting, drilling,reaming, resurfacing, or impacting instrument on the regions of thebone. The arthroplasty guide may, for example, include referencing rodsand one or more apertures and/or slots that are configured to acceptsuch an instrument. However, under some methods, it is difficult todetermine the proper orientation of an arthroplasty guide and ultimatelyof the positioning and alignment of an acetabular cup implant. Somemethods utilize arthroplasty guides to provide orientation of thetreatment relative to the regions of the bone. However, such guidesoften rely on a human to subjectively determine or “eyeball” rotationalangles and the extent of the treatment. For example, when performing anacetabular cup implantation into the hip region of a patient, manyguides rely on a surgeon to determine the proper orientation of theguide as well as how much of the bone to remove when mating theimplanted prosthesis to the bone. More particularly, once a surgeon hasbegun reaming a patient's acetabulum or impacting/implanting theacetabular cup, it can be difficult and damaging to accurately stop thereaming or impacting/implanting and start anew.

Accordingly, there is a need in the art for a customized arthroplastyacetabular cup positioning guide, and surgical systems and methods forgenerating and employing the acetabular cup positioning guide thatincreases the accuracy of arthroplasty procedures.

SUMMARY OF THE INVENTION

Implementations described and claimed herein address the foregoingproblems by providing a customized acetabular cup positioning guide aswell as systems and methods for generating and employing the acetabularcup positioning guide for use in a hip replacement arthroplastyprocedure.

A custom acetabular positioning guide and method of manufacturing andemploying the guide are disclosed herein. In one implementation, theacetabular cup positioning guide includes: a directional rod extendingfrom a semi-hemispherical blank or mold, which has a hemisphericalsurface that is a negative of the surface contour of the inside surfaceof the patient's acetabulum. The manufactured shape-match hemisphericalsurface of the hip guide matingly interdigitates with the correspondinginner surface of the patient's acetabulum and causes the directional rodto extend along a directional line that mimics a preoperatively plannedaxis. The axis defined by the directional rod is then used as a guidefor implanting the prosthetic cup with an impactor shaft. While usingthe impactor shaft to drive the prosthetic cup into the acetabular cupof the patient, the surgeon tries to replicate the same orientation ofthe directional rod with the impactor rod.

In another implementation, the acetabular cup positioning guide includesa shape-match hip guide, which includes the directional rod andsemi-hemispherical blank with a hemispherical surface that is a negativecontour of the inside surface of the patient's acetabular cup, asdescribed in the previous implementation. In addition, the positioningguide includes a first coupler half of an outrigger device that extendsover the directional rod. A second coupler half of the outrigger deviceis coupled to the first coupler half as well as a reference rod thatextends through the second coupler half to be imbedded in the bone ofthe hip region. The reference rod is held parallel to the directionalrod by the outrigger device. The cup guide and directional rod areremoved from the outrigger device, which stays implanted into the hipregion of the patient in the original orientation. Subsequent to reamingthe acetabular cup, wherein the reaming angle of the reamer may beguided by the coupler, which attaches the first coupler to thedirectional rod or like device, the prosthetic acetabular cup is thenplaced in the patient's acetabular cup. The outrigger device providesone angle (i.e., inclination angle), whereby the surgeon “eyeballs” theother angle (i.e., aversion angle).

In another implementation, the acetabular cup positioning guide includesa shape-match hip guide, which includes the directional rod andsemi-hemispherical blank with a hemispherical surface that is a negativecontour of the inside surface of the patient's acetabular cup, asdescribed in the previous implementation. In addition, the positioningguide includes a silo device, which includes a barrel with a guide holethat slideably receives the directional rod. The silo device alsoincludes a plurality of silo legs that extend from the barrel and areadapted for anchoring to the bone of the patient's hip region. The silolegs can be anchored to the hip region by pins, screws, or otherdevices. Once anchored to the hip region, the shape-match hip guide canbe removed from the patient's acetabulum and thus the silo device. Thepatient's acetabulum is reamed in preparation for implantation of theprosthetic acetabular cup. The prosthetic acetabular cup is theninserted into the patient's acetabulum or acetabular cup and an impactoris inserted into the guide hole of the silo barrel via an access slotand is held in place against the prosthetic cup by reinstallation of akeyed side portion into the slot. As a result, the impactor is heldagainst the prosthetic cup in proper alignment as established by the rodof the shape-match hip guide. The impactor, which is slidingly retainedin the guide hole, may then be impacted against the prosthetic cup toseat the cup in the patient's acetabular cup. The silo and impactor canthen be removed, leaving behind the implanted prosthetic acetabular cup.

Other implementations described and claimed herein provide a method ofmanufacturing the custom acetabular cup positioning guide. In oneembodiment, the method of manufacturing the custom guide includesgenerating a plurality of MRI slices, CT slices, or other suitablemedical images of a portion of a patient's bone to undergo anarthroplasty procedure. These images are used in the pre-operativeplanning phase of the procedure and can include medical imaging inaxial, coronal, and sagittal planes.

In one embodiment of the method of manufacturing the custom acetabularcup positioning guide, the operation includes placing anatomicallandmarks around the bone boundaries in the medical image slices. Forexample, placing the landmark points may include a user at a userinterface employing at least one of a mouse, keyboard, pen-and-tabletsystem, touch screen system, or spatial input device to place landmarkpoints. The bone boundaries may include lines representative in themedical imaging slices of acetabular cup boundaries, among others.

In one embodiment of the method of manufacturing the custom acetabularcup positioning guide, the operation includes defining a triangle in acoronal image slice of the hip region of the patient that extendsbetween certain landmarks. The triangle can be defined across thepatient's anterior pelvic area, wherein the triangle's three corners arerespectively located at the right anterior-superior ilium symphysis(“ASIS-R”), the left anterior-superior ilium symphysis (“ASIS-L”), andthe pubic symphysis. A pelvic axis line is defined to extend across theright teardrop and the left teardrop of the pelvis. Both legs of thetriangle can be seen to extend immediately adjacent a proximal point ofthe acetabular cup. The triangle can additionally include a frontal axisthat divides the triangle at its height by extending between a midpointof the base line of the triangle that extends between the ASIS-R and theASIS-L. The frontal axis is used to check for pelvic tilt. A “check” canbe made that the frontal axis is perpendicular to the pelvic axis.Additional measurements can be taken with respect to the triangle; themeasurements can include determining the angle between the pelvic axisand the target side line, wherein the target side line is the leg of thetriangle that extends between the pubic symphysis and theanterior-superior ilium symphysis on the surgical target side (i.e.,ASIS-R or ASIS-L). A 45 degree angle or any value that is required as asurgical goal prescribed by the surgeon can also be defined between anaxis line and the pelvic axis, wherein the intersection of the axis lineand the pelvic axis is about the teardrop of the pelvis on the surgicaltarget side. The 45 degree angle that was just described can be moved tointersect the target side line in such a manner that the axis lineprojects generally along the axis of the femoral head and the femoralneck of the surgical target side. The axis line now generally defines ahip guide pin axis, which defines the inclination of the prostheticacetabular cup.

In one embodiment of the method of manufacturing the custom acetabularcup positioning guide, the operation includes converting the MRI slices,CT slices, or similar medical images into at least one three dimensionalmodel that represents the portion of the patient's body to undergo anarthroplasty procedure. The three dimensional model can include aportion of the pelvis and the contour surface of the acetabular cup, thecontour surface being a generally identical replication of the innersurface of the patient's acetabular cup or acetabulum. The pre-operativeplanning process explained with respect to the two dimensional medicalslices is replicated with respect to the three dimensional model. Aplane connects the proximal point of the public symphysis with aproximal point of the acetabular cup. A second plane is provided suchthat it intersects the first plane at the proximal point of theacetabular cup. The second plane, also referred to as an inclinationplane, extends through the center point of the acetabular cup. A thirdplane, referred to as an anteversion plane, is positioned to evenlydivide the anterior and posterior walls of the acetabular cup and alsopass through the center of the acetabular cup. The anteversion plane isperpendicular to the inclination plane and it divides the acetabular cupin half. The intersection of the two planes defines an axis line thatapproximates a center axis of the acetabular cup.

In one embodiment of the method of manufacturing the custom acetabularcup positioning guide, the operation includes a three dimensional modelof a candidate prosthetic acetabular cup occupying the acetabular cup ofthe three dimensional surface model. The prosthetic cup is positionedrelative to the inclination and anteversion planes such that a centeraxis of the cup is coaxial with the axis defined by the intersection ofthe planes. A three dimensional model of a directional rod can beincluded, wherein the directional rod is positioned so as to be coaxialwith the axis defined by the intersection of the planes.

In one embodiment of the method of manufacturing the custom acetabularcup positioning guide, the operation includes replacing the threedimensional model candidate prosthetic cup with a three dimensionalmodel of a semi-hemispherical blank or mold, while maintaining thedirectional rod in its orientation relative to the intersection of theinclination and anteversion planes. The hemispherical surface of thesemi-hemispherical blank or mold extends along the surface contour ofthe inside surface of the acetabular cup of the three dimensionalsurface model. As a result, the blank or mold is caused to assume asurface contour that is a negative of the surface contour of the insidesurface of the acetabular cup of the three dimensional surface model.

Other implementations are also described and recited herein. Further,while multiple implementations are disclosed, still otherimplementations of the presently disclosed technology will becomeapparent to those skilled in the art from the following detaileddescription, which shows and describes illustrative implementations ofthe presently disclosed technology. As will be realized, the presentlydisclosed technology is capable of modifications in various aspects, allwithout departing from the spirit and scope of the presently disclosedtechnology. Accordingly, the drawings and detailed description are to beregarded as illustrative in nature and not limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a system for employing the customizedacetabular cup guide production method disclosed herein.

FIGS. 1B-1E are flow chart diagrams outlining the acetabular cuppositioning guide production method disclosed herein.

FIGS. 1F-1G are flow chart diagrams outlining the surgical method ofemploying the acetabular cup positioning guide.

FIGS. 1H-1I are flow chart diagrams outlining the surgical method ofemploying the acetabular cup positioning guide with an outrigger device.

FIGS. 1J-1K are flow chart diagrams outlining the surgical method ofemploying the acetabular cup positioning guide with a silo device.

FIG. 2A illustrates a series of medical imaging scan slices generatedvia MRI, CT or other medical imaging techniques.

FIG. 2B is a table of MRI scanning parameters used in the generation ofthe medical image slices depicted in FIG. 2A.

FIGS. 3A and 3B are, respectively, axial and sagittal plane medicalimage slices of the patient's acetabular cup.

FIG. 4 is an axial plane medical image slice exemplary of the imagecontrast in the various image slices.

FIG. 5 is a coronal plane medical image slice of the entire hip regionused in the preoperative planning stages of a hip replacement procedure.

FIGS. 6A-6F are coronal image slices depicting various landmarks andparameters used in the preoperative planning stages of a hip replacementprocedure to determine a hip guide pin axis that extends generally alongthe axis of the femoral head and the femoral neck on the surgical targetside of a patient.

FIG. 7 is an axial plane medical image slice segmented with a splinealong the inner surface of the acetabular cup.

FIG. 8 is another example of a medical image slice segmented with aspline along the inner surface of the acetabular cup.

FIG. 9 is a computer generated three dimensional surface model of apatient's acetabular cup compiled from various splines.

FIG. 10 is an enlarged view of the acetabular cup of the threedimensional model of a patient's acetabular cup.

FIG. 11 is an enlarged view of the acetabular cup of the threedimensional model that depicts possible inaccurate areas that form whenconverting two dimensional medical images into three dimensional models.

FIGS. 12A-12D are three dimensional surface models of a patient'sacetabular cup in a coronal plane, with similar landmarks and parametersemployed in FIGS. 6A-6F in determining a hip guide pin axis that extendsgenerally along the axis of the femoral head and the femoral neck on thesurgical target side of a patient.

FIGS. 13A-13B are three dimensional surface models of a patient'sacetabular cup wherein a candidate prosthetic acetabular cup without andwith a directional rod extending along the hip guide pin axis occupiesthe acetabular cup of the three dimensional surface model.

FIG. 14 is a three dimensional surface model of a patient's acetabularcup, similar to FIG. 13, wherein the candidate prosthetic acetabular cupis replaced in the acetabular cup of the 3D surface model by a 3D modelof a semi-hemispherical blank or mold.

FIG. 15 is a 3D model of a shape-match hip guide that includes adirectional rod extending from a semi-hemispherical blank or mold, whichhas the hemispherical surface that is a negative of the surface contourof the inside surface of the acetabular cup of the 3D surface model.

FIGS. 16A-16B are views of a patient's actual hip region including theacetabular cup in the process of receiving an actual prostheticacetabular cup via a shape-match hip guide.

FIGS. 17A-17G are views of a patient's actual hip region including theacetabular cup in the process of receiving an actual prostheticacetabular cup via a shape-match hip guide and an outrigger device usedin aligning the reaming of the patient's acetabular cup and/orimplantation of a prosthetic acetabular cup.

FIG. 18A-18G are views of a patient's actual hip region including theacetabular cup in the process of receiving an actual prostheticacetabular cup via a shape-match hip guide and a silo device used inaligning the reaming of the patient's acetabular cup and/or implantationof a prosthetic acetabular cup.

FIG. 19 illustrates three different embodiments of the custom fit matinghead of the hip guide described herein.

FIG. 20 depicts four different potential mating surface regions that mayor may not be integrated into the mating surface of the head of the hipguide described herein.

DETAILED DESCRIPTION

Aspects of the presently disclosed technology involve customizedacetabular cup guides 252, systems 3, and methods of using the sameduring arthroplasty procedures. In one aspect, the guides 252 arecustomized to fit specific bone surfaces of a hip joint 12 of a specificpatient 11 to treat (e.g., cut, drilled, reamed, and/or resurfaced) thebone to provide one or more surfaces that can align with an implant andthereby accommodate the implant.

For an overview discussion of the systems 3 for, and methods ofproducing the customized acetabular cup positioning guides 252,reference is made to FIG. 1A. FIG. 1A is a schematic diagram of a system3 for employing the customized acetabular cup guides production methoddisclosed herein. FIGS. 1B-1E are flow chart diagrams outlining theacetabular cup positioning guide production method disclosed herein. Thefollowing overview discussion can be broken down into four sections.

The first section, which is discussed with respect to FIGS. 1A-1C,pertains to an example method of determining, from two dimensional (2D)medical images, a hip guide pin axis line for use in the preoperativeplanning stages of an arthroplasty procedure. The hip guide pin axisline generally extends along the patient specific axis of the femoralhead and femoral neck, wherein a prosthesis that is implanted withrespect to the hip guide pin axis line will restore the patient's jointto its pre-degenerative orientation. In other words, in someembodiments, the patient's joint may be restored to its naturalalignment, whether valgus, varus or neutral.

The system 3 for producing the customized guide 252 may be such that thesystem 3 initially generates the preoperative planning (“POP”)associated with the jig in the context of the POP resulting in thepatient's hip being restored to its natural alignment. The disclosure,however, should not be limited to methods resulting in natural alignmentonly, but should, where appropriate, be considered as applicable tomethods resulting in alignments other than a natural alignment.

The second section, which is discussed with respect to FIGS. 1A and1D-1E, pertains to an example method of generating a three dimensional(3D) bone model of a portion of a patient's body to undergo a hipreplacement procedure, in particular a patient's acetabular cup, andgenerating a 3D shape-match hip guide model with a head that is anegative of the surface contour of a patient's acetabular cup and adirectional rod that aligns with the hip guide pin axis line when thehead matingly interdigitates with the patient's acetabular cup. The 3Dshape-match hip guide model can then be machined in a CNC machine 13 orother suitable rapid prototype machine to produce a custom guide 252,which is sent to the surgeon, and employed in an arthroplasty surgicalprocedure.

The third section, which is discussed with respect to FIGS. 1A and1F-1K, pertains to a method of employing the shape-match guide in asurgical procedure. In certain embodiments, the shape-match hip guide isemployed by itself and in certain embodiments the shape-match hip guideis employed in conjunction with an outrigger or silo alignment device.

The fourth section, which is discussed with respect to FIGS. 19-20,pertains to the mating head surface of the custom acetabular hip guide252 as it relates to placement in a patient's acetabular cup.

I. POP with 2D Medical Images.

The system 3 in FIG. 1A includes a computer 4 having a CPU 5, a monitoror screen 1 and operator interface controls 6. The computer 4 is linkedto a medical imaging system 7, such as a CT or MRI machine 7, and acomputer controlled machining system 13, such as a CNC milling machine13 or other rapid prototype machine (e.g., stereolithography apparatus[“SLA” Machine]). As indicated in FIG. 1A, a patient 11 has a hip joint12 to be replaced. The patient 11 has the joint 12 scanned in theimaging machine 7. The imaging machine 7 makes a plurality of scans 10of the joint 12, wherein each scan pertains to a thin slice of the joint12.

As can be understood from FIGS. 1B and 2A the plurality of scans 10 isused to generate a plurality of 2D images of the joint [BLOCK 100].Where, for example, the joint is a hip 12, the 2D images will includethe femur, acetabular cup, and pelvic area generally. The imaging may beperformed via CT or MRI 7.

As can be understood from FIGS. 1A and 1D, the 2D images [BLOCK 100] aresent to the computer 4 for creating computer generated 3D models [BLOCK150], which are used to generate a 3D shape-match hip guide model 240.FIG. 2A illustrates a series of medical imaging scan slices 10 generatedvia MRI, CT 7 or other medical imaging techniques. These image slices 10are employed in the preoperative planning and shape-match hip guidedesigning methodology discussed in the following pages.

FIG. 2B is a table of MRI scanning parameters used in the generation ofthe image slices 10 depicted in FIG. 1A.

FIGS. 3A and 3B are, respectively, axial and sagittal MRI image slices10 of the patient's acetabular cup 30 at the most axial and sagittalrepresentative cross section of the cup 30. In other words, the imagesslices 10 of FIGS. 3A and 3B are at those axial and sagittal crosssections that show the cup 30 at its largest diameter and most roundedpoint as viewed axially and sagittally, respectively. The boundary ofthe cup 30 can be determined in the axial and sagittal cross-sectionalslices illustrated in FIGS. 3A and 3B [BLOCK 105]. The bone boundariesare segmented to create bone contour lines. FIG. 7 illustrates anexample of how each of the MRI image slices 10 is segmented with aspline 120 along the inner surface 40 of the acetabular cup 30. Thespline 120 includes control points 122.

As shown in FIGS. 3A and 3B, a MRI locator or reference line 32 ispositioned so as to extend across a widest part of the cup 30 at thearticular edges 34 of the cup 30. A coronal scan angle, which isindicated by the multiple parallel scan lines 36 in each of the axialand sagittal image slices 10, is set to be perpendicular to each of theaxial and sagittal MRI locator lines 32 in the respective axial andsagittal MRI image slices 10 depicted in FIGS. 3A and 3B. Thus, thecoronal scan angle is set to be perpendicular to each of the axial andsagittal reference lines 32 that connect the articulate edges 34 in themost representative cross section of the cup 30. The fovea 38 andfemoral head 39 can be seen clearly in FIG. 3A. The fovea 38 is therecess or non-spherical area of the cup 30 and is the part of the cup 30that gives a tactile feel and prevents displacement of the matingsurface 232 (shown in FIG. 15) of the shape-match hip guide 240 when thesurface 232 is in mating surface contact with the cup 30, as describedin the following pages.

FIG. 4 illustrates a MRI image slice 10 exemplary of the image contrastin the various image slices. The MRI imaging parameters, including TRand TE values are set to make the ideal contrast for the anatomicaldetails of the inner surface 40 of the cup 30 and, especially, the fovea38.

As indicated in FIG. 1B, landmarks are identified on the 2D medicalimages [BLOCK 110]. FIG. 5 illustrates a coronal CT image slice 50 ofthe entire hip area 52 of the patient. This coronal view of the entirehip area 52 is used for preoperative planning, as described as follows.The acetabular cups 30 and the femoral heads 39, along with other usefulanatomical landmarks are clearly visible in the CT image slice 50. Thelandmarks are identified and used to determine a hip axis guide linethat will be used in conjunction with the 3D bone model in generating a3D shape-match hip guide model.

FIG. 6A is the same coronal CT image slice 50 of FIG. 5, except atriangle 60 has been defined thereon extending between certain landmarks[BLOCK 115]. Specifically, the preoperative planning methodology beginsby defining the triangle 60 across the patient's anterior pelvic area.The triangle's three corners are respectively located at the rightanterior-superior ilium symphysis (“ASIS-R”) 62, the leftanterior-superior ilium symphysis (“ASIS-L”) 64, and the pubic symphysis66. Further, a pelvic axis line 67 is defined to extend across the rightteardrop 68 and the left teardrop 69 of the pelvis [BLOCK 120]. Bothlegs of the triangle 60 (i.e., the sides of the triangle 60 extendingbetween the pubic symphysis and a respective ASIS) can be seen to extendimmediately adjacent a proximal point 63 of the acetabular cup 30.

FIG. 6B is the same coronal CT image slice 50 of FIG. 6A, except thetriangle 60 has been divided at its height by a frontal axis 70 [BLOCK125]. As illustrated in FIG. 7, the frontal axis 70 extends between amidpoint 71 of the base line 72 of the triangle 60 that extends betweenthe ASIS-R 62 and ASIS-L 64. The steps of the preoperative planningdescribed with respect to FIGS. 6 and 7 is used to check for pelvictilt. For example, if the hip joint cartilage is damaged, there will bepelvic tilt such that the pelvic axis 67 and base line (the topmostline) 72 of the triangle 60 will not be substantially parallel.

FIG. 6C is the same coronal CT image slice 50 of FIG. 6B, except a checkis made to see if the frontal axis 70 and the pelvic axis 67 areperpendicular to each other [BLOCK 130].

FIG. 6D is the same coronal CT image slice 50 of FIG. 6C, except ameasurement is conducted on the patient's surgical target side 90 todetermine the angle 92 between the target side line 94 and the pelvicaxis 67 [BLOCK 135]. The target side line 94 is the leg of the triangle60 that extends between the pubic symphysis 66 and the anterior-superiorilium symphysis on the surgical target side 90. Thus, since the surgicaltarget side 90 in the example provided in FIG. 6D is the left side ofthe patient, the target side line 94 extends between the pubic symphysis66 and the ASIS-L 64. As indicated in FIG. 6D, the triangle point at thepubic symphysis 66 can be at the superior extent 66 of the pubicsymphysis in one embodiment. In other embodiments, the triangle point atthe pubic symphysis 66A can be at the inferior extent 66A of the pubicsymphysis. In one embodiment, what is considered an appropriate valuefor the angle 92 in a healthy patient may be a value provided by thesurgeon based on the surgeon's examination of the patient and medicalimages of the patient. In other embodiments, the triangle point at thepubic symphysis 66A can be at the inferior extent 66A of the pubicsymphysis. In another embodiment, what is considered an appropriatevalue for the angle 92 in a healthy patient may be a value provided bymedical texts or experts.

FIG. 6E is the same coronal CT image slice 50 of FIG. 6D, except a 45degree angle 100 is defined between an axis line 102 and the pelvic axis67, the intersection of the axis line 100 and the pelvic axis 67 beingat the teardrop of the pelvis on the surgical target side 90 [BLOCK140]. Since the surgical target side 90 is on the patient's left side inthis example, the left teardrop 69 is the intersection of the axis line102 and the pelvic axis 67.

FIG. 6F is the same coronal CT image slice 50 of FIG. 6E, except the 45degree angle 100 has been added to the angle 92 defined in FIG. 6D andthe axis line 102 has been moved to intersect the target side line 94 insuch a manner that the axis line 102 projects generally along the axisof the femoral head 39 and the femoral neck on the surgical target side90 [BLOCK 145]. The axis line 102 now generally defines a hip guide pinaxis 202 as detailed in the following discussion pertaining to FIGS. 13Aand 13B. This hip guide pin axis 202 defines the inclination of theprosthetic acetabular cup 210 as described in the following discussionpertaining to FIGS. 13A and 13B.

II. POP with 3D Bone Model.

The 2D medical images can be used to generate a 3D bone model of thearea of the patient to undergo an arthroplasty procedure. As shown inFIG. 7, the MRI image slices 10 are segmented with a spline 120 alongthe inner surface 40 of the acetabular cup 30, wherein the spline 120includes control points 122. The segmented 2D images and the associatedsplines 120 and control points 122 are used to generate a 3D bone model.The 3D bone model depicts the bones in the present deterioratedcondition with their respective degenerated joint surfaces, which may bea result of osteoarthritis, injury, a combination thereof, etc. FIG. 8illustrates how the MRI image slices 10 are segmented with a spline 120that includes control points 122 at the inner surface 40 of theacetabular cup 30, near the anterior and the posterior walls.

Computer programs for creating 3D computer generated bone models fromsegmented 2D images include: Analyze from AnalyzeDirect, Inc., OverlandPark, Kans.; Insight Toolkit, an open-source software available from theNational Library of Medicine Insight Segmentation and RegistrationToolkit (“ITK”), www.itk.org; 3D Slicer, an open-source softwareavailable from www.slicer.org; Mimics from Materialise, Ann Arbor,Mich.; and Paraview available at www.paraview.org. Further, someembodiments may use customized software such as OMSegmentation (renamed“PerForm” in later versions), developed by OtisMed, Inc. TheOMSegmentation (or PerForm) software may extensively use “ITK” and/or“VTK” (Visualization Toolkit from Kitware, Inc., available atwww.vtk.org). Some embodiments may include using a prototype ofOMSegmentation, and such may utilize InsightSNAP software.

As indicated in FIG. 1D, the 3D computer bone models are generated from2D medical images in the preoperative planning stages of an arthroplastyprocedure [BLOCK 150]. FIG. 9 depicts a computer generated threedimensional surface model 130 compiled from the various splines 120. The3D surface model 130 includes a portion of the pelvis and the contoursurface 132 of the acetabular cup 30, the contour surface 132 being agenerally identical replication of the inner surface 40 of the patient'sacetabular cup 30.

FIG. 10 is an enlarged view of the acetabular cup 30 of the 3D surfacemodel 130 of FIG. 13, wherein the fovea 38 is more clearly depicted. Asalready noted, the fovea 38 is the recess or non-spherical area of theinner surface 40 of the cup 30 and is the part of the cup 30 that givesa tactile feel and prevents displacement of the mating surface 232(shown in FIG. 15) of the shape-match hip guide 252 when the surface 232is in mating surface contact with the cup 30, as described in thefollowing paragraphs. In one embodiment, the methodology includeschecking the surface features of the fovea 38 to see if the trending ofthe outlines are consistent based on the MRI image analysis.

As can be understood from FIG. 8, the medical imaging scan angledescribed in FIGS. 3A and 3B can limit the accuracy of the anterior andposterior wall segmentation. As a result, the corresponding 3D model 130has inaccuracies in the anterior and posterior regions of the cup 30.These inaccurate areas of the 3D model 130 are enclosed by therectangles 160, 161 in FIG. 11, which is the same enlarged view of thecup 30 of the 3D model 130 of FIG. 10. These inaccurate areas may besubjected to an “overestimation” process as described in U.S. patentapplication Ser. No. 12/505,056, filed Jul. 17, 2009 and herebyincorporated by reference in its entirety into the present application.By overestimating the inaccurate areas, the portions of the matingsurface 232 of the shape-match hip guide 252 corresponding to theinaccurate areas will not make surface contact the patient's cup innersurface corresponding to the inaccurate regions when the mating surface232 matingly engages other portions of the patient's inner cup surface[BLOCK 155].

FIG. 12A is the 3D surface model 130 of FIG. 9 shown in the same coronalview used in FIGS. 6A-6F. The planning process explained with respect tothe coronal CT scan 50 of FIGS. 6A-6F will now be replicated withrespect to the 3D model 130. Thus, as shown in FIG. 12A, a plane 170connects the proximal point of the pubic symphysis 66 with a proximalpoint 63 of the acetabular cup 30 [BLOCK 165]. Thus, the plane extendsfrom the pubic symphysis 66 to a point 63 near the fovea, therebyreplicating the geometry of the planning step described with respect toFIG. 6A.

FIG. 12B is the 3D surface model 130 of FIG. 12A further along in theplanning process replication. As shown in FIG. 12B, a second plane 180is provided such that the second plane 180 intersects the first plane170 at the proximal point 63 of the acetabular cup 30 [BLOCK 170]. Thus,the second plane 180 is oriented to mimic the trajectory of the axis 102of FIG. 6F, thereby replicating the geometry of the planning stepdescribed with respect to FIG. 6F.

FIG. 12C is the 3D surface model 130 of FIG. 12B with the same planes170, 180, but rotated so as to show the model 130 from a more inferiorand lateral perspective. As illustrated in FIG. 12C, the second plane180, which may be called an inclination plane 180, extends through thecenter point of the acetabular cup 30. In one embodiment, the view ofthe model 130 provided in FIG. 12C may be considered perpendicular tothe coronal view depicted in FIG. 12B.

FIG. 12D is the 3D surface model 130 of FIG. 12C with the same planes170, 180 and further including a third plane 200, which may be calledthe anteversion plane 200 [BLOCK 175]. As illustrated in FIG. 12D, theanteversion plane 200 is positioned to evenly divide the anterior andposterior walls of the acetabular cup 30 and also pass through thecenter of the acetabular cup 30. The anteversion plane 200 isperpendicular to the 45 degree line plane (i.e., the inclination plane180). Also, the anteversion plane 200 divides the inclination plane 180in half. The intersection of the two planes 180, 200 defines an axisline 202 that approximates a center axis of the acetabular cup 30.

FIG. 13A illustrates the 3D surface model 130 of FIG. 12D furtherrotated with the same planes 170, 180, 190 and further including a 3Dmodel of a candidate prosthetic acetabular cup 210 occupying theacetabular cup 30 of the 3D surface model 130 [BLOCK 180]. Theprosthetic cup 210 is positioned relative to the inclination andanteversion planes 180, 200 such that a center axis of the cup iscoaxial with the axis 202 defined by the intersection of the planes 180,200. Thus, the placement of the 3D model of the prosthetic cup 210 inthe cup 30 of the 3D surface model 130 relative to the axis 202 resultsin the preoperative planning of the surgical placement of an actualprosthetic acetabular cup in the actual acetabular cup of the patient.

FIG. 13B illustrates the 3D surface model 130 of FIG. 13A wherein theplanes 180, 190 have been removed and a 3D model of a directional rod220 has been coupled to the interior surface of the 3D model of thecandidate prosthetic acetabular cup 210 occupying the acetabular cup 30of the 3D surface model 130. The directional rod 220 is positioned so asto be coaxial with the axis 202 defined by the intersection of theplanes 180, 200 in FIG. 13A. Thus, the placement of the 3D model of thedirectional rod 220 to be coaxial with the axis 202 defined by theintersection of the planes 180, 200 in FIG. 13A replicates theinclination angle from the preoperative planning depicted in FIG. 6F.

FIG. 14 illustrates the 3D surface model 130 of FIG. 13B wherein all theplanes 170, 180, 190 have been removed, the 3D model of the directionalrod 220 is still coaxially positioned relative to the axis 202 asdescribed with respect to FIG. 13B and the 3D model of the candidateprosthetic acetabular cup 210 has been replaced in the acetabular cup 30of the 3D surface model 130 by a 3D model of a semi-hemispherical blankor mold 230 [BLOCK 185]. The hemispherical surface 232 of thesemi-hemispherical blank or mold 230 extends along the surface contourof the inside surface of the acetabular cup 30 of the 3D surface model130. As a result, the hemispherical surface 232 of thesemi-hemispherical blank or mold 230 is caused to assume a surfacecontour that is a negative of the surface contour of the inside surfaceof the acetabular cup 30 of the 3D surface model 130.

FIG. 15 illustrates the completed 3D model of a shape-match hip guide240 including the directional rod 220 extending from thesemi-hemispherical blank or mold 230, which has the hemisphericalsurface 232 that is a negative of the surface contour of the insidesurface of the acetabular cup 30 of the 3D surface model 130. Thus, whenan actual shape-match hip guide 252 is manufactured to match the modelguide 240, the shape-match hemispherical surface of the actual hip guide252 will matingly interdigitate with the corresponding inner surface ofthe patient's acetabular cup and cause the directional rod 220 to beextend along a directional line that mimics the axis 202 preoperativelyplanned according to the steps outlined in FIGS. 6A-6F and 12A-14.

As illustrated in FIG. 1E, the 3D model shape-match hip guide 240 issent to a CNC machine 13 or other suitable prototyping machine in orderto machine or produce a physical shape-match hip guide 252 [BLOCK195-200]. Data associated with the 3D model shape-match hip guide 240can be transferred to a storage medium (e.g., compact disc, digitalvideo disc, flash drive) and physically delivered to a manufacturer orthe data can be electronically sent via a network connection to amanufacturer. Alternatively, the computer that generates the 3D modelshape-match hip guide 240 can be directly connected to a CNC machine 13for machining of the physical shape-match guide 252. The mating surface232 of the hip guide 252 can be machined by an additive process, such asby a rapid prototyping machine, or by a reductive process, such as bymachining in a CNC machine 13. In the case of a machining process in aCNC machine 13 or similar device, a guide blank 51 will be inputted intothe CNC machine 13 and the machine will generate the customized matingsurface 232 of the blank or mold 51.

In one embodiment, the POP procedure is a manual process, whereincomputer generated 3D bone models are manually manipulated by a personsitting in front of a computer and visually observing the bone model andthe generation of the model shape-match hip guide 240 via the computercontrols. In one embodiment, the bone modeling process is generally orcompletely automated. In other words, a computer program may analyze thebone models and their degenerated surface to determine the stepsinvolved in the preoperative planning process of the procedure (e.g., acomputer may perform the “overestimation” process and generate anappropriate bone model).

III. Operating Procedure.

Once the POP phase of the procedure is complete and a physicalshape-match guide 252 is generated, a surgeon can perform thearthroplasty procedure with the shape-match guide 252.

A. Employing the Shape-Match Hip Guide.

A first embodiment of a method of employing the guide 252 will now bediscussed. In preparation for the arthroplasty procedure, the region ofa patient's body to undergo the procedure is prepared for surgery [BLOCK205]. The preparation can include a surgeon or a surgical assistantmaking the appropriate incisions into the target area of the patient'sbody 12. Once the target area 12 is accessible for the procedure, theactual shape-match hip guide 252 is matingly received in the patient'sacetabular cup [BLOCK 210]. FIGS. 16A and 16B are inferior-lateral viewsof a patient's actual hip region 250 including the surgical targetacetabular cup 251 in the process of receiving an actual prostheticacetabular cup 260. As shown in FIG. 16A, an actual shape-match hipguide 252 is matingly received in the acetabular cup 251. The hip guide252 includes a directional rod 253 extending from a semi-hemisphericalhead 254 having a hemispherical surface that is a surface negative ofthe surface contour of the inside surface of the surgical targetacetabular cup 251. The guide 252 is manufactured to be generally anexact physical replica of the preoperatively planned 3D model guide 240of FIG. 15.

As can be understood from FIGS. 16A and 16B, the mating surface of thehead 254 of the guide 252 is interdigitated with the inner surface ofthe acetabular cup 251 to matingly engage with the inner surface suchthat the rod 253 extends from the cup 251 as preoperatively planned anddiscussed with respect to FIG. 15. The surgeon estimates the orientationof the rod 253 as depicted in FIG. 16A and then removes the guide 252from the cup 251 [BLOCK 215]. The surgeon then reams the acetabular cup251 [BLOCK 220]. The surgeon tries to replicate the same orientation ofthe rod 253 shown in FIG. 16A with the reamer [BLOCK 225].

As can be understood from FIG. 16B, once the reaming is complete, thesurgeon then inserts the prosthetic cup 260 into the acetabular cup 251via an impactor shaft 262 supporting the cup 260 [BLOCK 230]. Whileusing the shaft 262 to drive the prosthetic cup 260 into the acetabularcup 251, the surgeon tries to replicate the same orientation of the rod253 shown in FIG. 16A with the impactor rod 262 used in FIG. 16B [BLOCK235]. The surgeon then removes the impactor from the target area [BLOCK236].

B. Employing the Shape-Match Hip Guide with an Outrigger AlignmentDevice.

A second embodiment of a method employing the guide 252 will now bediscussed. In preparation for the arthroplasty procedure, the region ofa patient's body to undergo the procedure is prepared for surgery [BLOCK240]. The preparation can include a surgeon making the appropriateincisions into the target area of the patient's body. Once the targetarea is accessible for the procedure, the actual shape-match hip guide252 is matingly received in the patient's acetabular cup [BLOCK 245].FIGS. 17A and 17B are views of the patient's actual hip region 250including the surgical target acetabular cup 251 in the process ofreceiving an actual prosthetic acetabular cup via another method inconjunction with an outrigger device for employing the actualshape-match hip guide 252. As shown in FIGS. 17A and 17B, the actualshape-match hip guide 252 is matingly received in the acetabular cup 251as described with respect to FIG. 16A, and a first coupler half 270 ofthe outrigger device extends over the rod 253.

FIGS. 17C and 17D are views of the patient's actual hip region 250further illustrating the process of employing the outrigger device 300with the shape-match hip guide 252. As shown in FIGS. 17C and 17D, asecond coupler half 290 is coupled to the first coupler half 270, and areference rod 292 extends through the second coupler half 290 to beimbedded in the bone of the superior hip region 250 [BLOCK 250-255]. Thefirst and second coupler halves 270, 290 and the reference rod 292 arethe major components of the outrigger device 300. The reference rod 292is held parallel to the rod 253 of the guide 252 by the outrigger device300 [BLOCK 255].

FIG. 17E is a view of the patient's actual hip region 250 furtherillustrating the process of employing the outrigger device 300 with theshape-match hip guide 252. As shown in FIG. 17E, the hip guide 252 isremoved from the acetabular cup 251 and the outrigger device 300 whilemaintaining the outrigger device 300 in the same orientation andlocation shown in FIG. 17E via the reference rod 292 being imbedded inthe bone of the patient's hip region 250 [BLOCK 260]. Subsequent toreaming the acetabular cup 251 wherein the reaming angle of the reamermay be guided by the coupler 270, the prosthetic acetabular cup 260 isthen placed in the patient's acetabular cup 251 [BLOCK 265-270]. Theoutrigger device 300 only provides one angle (i.e., the inclinationangle), the surgeon having to determine the other angle (i.e., theanteversion angle).

FIG. 17F is a view of the patient's actual hip region 250 furtherillustrating the process of employing the outrigger device 300 with theshape-match hip guide 252. As shown in FIG. 17F, the impactor rod 262 isplaced against the inside of the prosthetic cup 260 and received in thefirst coupler half 270 previous occupied by the rod 253 of the hip guide252 as discussed with respect to FIGS. 17A and 17B [BLOCK 275]. Theoutrigger device 300 maintains the impactor rod 262 in the sameorientation and location of the rod 253 of the hip guide 252 on accountof the reference rod 292 being imbedded in the bone of the patient's hipregion 250. As already noted, the outrigger device 300 only provides oneangle (i.e., the inclination angle), the surgeon having to eyeball theother angle (i.e., the anteversion angle).

FIG. 17G is a view of the patient's actual hip region 250 illustratingthe impactor rod 262 ready for impaction of the prosthetic cup 260 intothe patient's acetabular cup 251 after removal of the outrigger device300 from the impactor rod 262 after the outrigger device 300 was used toalign the impactor rod 262 as described with respect to FIG. 17F. Theprosthetic acetabular cup is impacted into the patient's acetabular cup[BLOCK 280]. Following impaction, the impactor and outrigger device areremoved from the patient's acetabulum [BLOCK 281].

C. Employing the Shape-Match Hip Guide with a Silo Alignment Device.

A third embodiment of a method employing the guide 252 will now bediscussed. FIGS. 18A and 18B are views of the patient's actual hipregion 250 illustrating the process of employing a silo device 350 withthe shape-match hip guide 252. In preparation for the surgicalprocedure, a surgeon or a surgeon's assistant will prepare the hipregion of the patient for the procedure [BLOCK 285]. The preparation mayinclude making an incision and generally preparing the patient'sacetabulum to receive a prosthetic shape-match hip guide. As shown inFIG. 18A, the shape-match hip guide 252 is first matingly engaged withthe patient's acetabular cup 251 as previously described herein [BLOCK290]. As indicated in FIG. 18B, the barrel 351 of the preassembled silo350 is slid over the rod 253 of the guide 252, and the three silo legs350A-C extending from the silo barrel 351 are positioned for anchoringto the bone of the patient's hip region 250 [BLOCK 295].

FIGS. 18C and 18D are views of the patient's actual hip region 250further illustrating the process of employing a silo device 350 with theshape-match hip guide 252. As shown in FIG. 18C, the three silo legs350A-C extending from the silo barrel 351 are anchored to the bone ofthe patient's hip region 250 via pins 370A-C, thereby securing the silobarrel guide hole 372 in the alignment of the guide rod 253 [BLOCK 295].The barrel 351 includes a keyed side portion 374 that can be slidinglyremoved from the rest of the barrel 351 to reveal a side access slot 376[BLOCK 300]. As indicated in FIG. 18D, the keyed side portion 374 hasbeen removed from the rest of the barrel 351 to reveal the side accessslot 376, and the shape-match hip guide 252 has been removed fromengagement with the barrel 351 and removed from the patient's acetabularcup 251, thereby leaving the silo 350 in a fixed position properlyaligned to guide an impactor. The silo device 350 may then be used toguide the reamer during the reaming of the acetabular cup 251 [BLOCK305].

FIGS. 18E and 18F are views of the patient's actual hip region 250further illustrating the process of employing a silo device 350 with theimpactor 262. As shown in FIG. 18E, with the three silo legs 350A-Cextending from the silo barrel 351 and anchored to the bone of thepatient's hip region 250 via pins 370A-C, the prosthetic acetabular cup260 is inserted into the patient's acetabular cup 251, which has alreadybeen reamed [BLOCK 315]. As illustrated in FIG. 18F, the impactor 262enters the guide hole 372 of the silo barrel 351 via the side accessslot 376 and is held in place against the prosthetic cup 260 byreinstallation of the keyed side portion 374 into the slot 376 [BLOCK320]. As a result, the impactor 262 is held against the prosthetic cup260 in proper alignment as established by the rod 253 of the hip guide252 in reference to FIG. 18C. The impactor 262, which is slidinglyretained in the guide hole 372, may then be impacted against theprosthetic cup 260 to seat the cup 260 in the patient's acetabular cup251 [BLOCK 325]. As indicated in FIG. 18G, the silo 350 and impactor 262can then be removed, leaving behind the implanted prosthetic acetabularcup [BLOCK 330].

As can be understood from a review of the three embodiments discussedwith respect to FIGS. 16A-16B, 17A-17G, and 18A-18F, the embodiment ofFIGS. 16A-16B may be considered a directional guide only, the embodimentof FIGS. 17A-17G may be considered a directional guide plus an outriggerdevice, and the embodiment of FIGS. 18A-18F may be considered adirection guide plus a silo device.

IV. Shape-Match Guide Head.

FIG. 19 illustrates three different embodiments of the custom fit matinghead of the prosthetic hip guide 252 described herein. The differentembodiments have the following benefits. A 50% and 33% rim overflowmodels make less fitment with indecisiveness. Non-overflow models makestronger and unique positioning because of the exclusion of theinaccurate anterior and posterior regions for the mating surface at thesegmentation process illustrated in FIG. 8.

FIG. 20 depicts four different potential mating surface regions that mayor may not be integrated into the mating surface of the head of the hipguide 252 described herein. Area A is irregular and somewhat unreliableas a mating surface. Area B is a suitable mating surface. Area C isillustrative of the fovea. Area D is considered an extra opportunity fora mating surface of the head of the hip guide.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the spirit and scope of thepresently disclosed technology. For example, while the embodimentsdescribed above refer to particular features, the scope of thisdisclosure also includes embodiments having different combinations offeatures and embodiments that do not include all of the describedfeatures. Accordingly, the scope of the presently disclosed technologyis intended to embrace all such alternatives, modifications, andvariations together with all equivalents thereof.

What is claimed is:
 1. A method of manufacturing a custom acetabular cuppositioning guide for use in an arthroplasty procedure on a portion of ahip region of a patient's body, wherein the portion of the hip regionincludes a patient's acetabular cup, the method of manufacturingcomprising: generating a plurality of two dimensional medical images ofthe portion of the hip region of the patient's body to undergo thearthroplasty procedure; identifying landmarks on bone boundaries in thetwo dimensional medical images; identifying a hip axis line bytriangulating a plurality of the landmarks in the two dimensionalmedical images; using a computer processor to generate a threedimensional bone model of the portion of the hip region of the patient'sbody to undergo the arthroplasty procedure from the plurality of twodimensional medical images, wherein the three dimensional bone modelincludes a three dimensional model of the patient's acetabular cup;shape-matching an inside surface of the three dimensional model of thepatient's acetabular cup relative to the hip axis line; generating thecustom acetabular positioning guide based upon the identification of thehip axis line and a negative contour of the inside surface of the threedimensional model of the patient's acetabular cup.
 2. The method ofclaim 1, wherein the custom positioning guide comprises a directionalrod that extends generally along the hip axis line when the custompositioning guide matingly interdigitates with an inside surface of thepatient's acetabular cup.
 3. The method of claim 1, further comprisinggenerating a three dimensional acetabular cup positioning guide modelfrom the three dimensional bone model.
 4. The method of claim 1, whereinthe plurality of medical images are generated from MRI slices or CTslices.
 5. The method of claim 1, wherein identifying landmarks on boneboundaries include a user at a user interface employing at least one ofa mouse, keyboard, pen-and-tablet system, touch screen system, orspatial input device to place landmark points.
 6. The method of claim 1,wherein the landmarks identified on the bone boundaries in the twodimensional images comprise a left teardrop and a right teardrop of apelvis, a right anterior-superior ilium symphysis (“ASIS-R”), a leftanterior-superior ilium symphysis (“ASIS-L”), and a pubic symphysis. 7.The method of claim 6, wherein the landmarks are identified in a coronalimage slice.
 8. The method of claim 6, wherein the plurality oflandmarks used in triangulation in the two dimensional images includethe ASIS-R, the ASIS-L, and the pubic symphysis.
 9. The method of claim8, wherein identifying the hip axis line further comprises identifying apelvic axis line in the two dimensional images that extends through theleft teardrop and the right teardrop of the pelvis.
 10. The method ofclaim 9, further comprising determining an acute first angle between thepelvic axis line and a first line that extends through the pubicsymphysis and either the ASIS-R or ASIS-L, wherein the first line willextend through the ASIS-R if a right hip region is to undergo thearthroplasty procedure and the first line will extend through the ASIS-Lif a left hip region is to undergo the arthroplasty procedure.
 11. Themethod of claim 10, further comprising identifying a second angle byincreasing the first angle by a surgically prescribed degree, rotateddownward from the first line, wherein the second angle is coextensivewith a hip axis angle, whereby the hip axis angle is defined between thefirst line and the hip axis line.
 12. The method of claim 11, whereinthe surgically prescribed degree is about forty-five degrees.
 13. Amethod of manufacturing a custom acetabular cup positioning guide foruse in an arthroplasty procedure involving a hip region of a patient'sbody, wherein the hip region includes the patient's femoral head,femoral neck and acetabular cup, the guide including a mating regionconfigured to matingly receive a portion of the patient's acetabularcup, the mating region including a surface contour that is generally anegative of a surface contour of the patient's acetabular cup, thesurface contour of the mating region being configured to mate with thesurface contour of the patient's acetabular cup in a generally matchingor interdigitating manner when the patient's acetabular cup is matinglyreceived by the mating region, the method of manufacture comprising: a)generating medical imaging slices of the portion of the patient bone; b)identifying landmarks on bone boundaries in the medical imaging slices;c) identifying a hip axis line, the hip axis line being generallycollinear with an axis of the patient's femoral head and femoral neck ina preoperative state, wherein the identifying the hip axis linecomprises triangulating landmarks on the bone boundaries in the medicalimaging slices; d) using a computer processor to generate a threedimensional bone model of the patient's acetabular cup; e)shape-matching an inner surface of the three dimensional bone model ofthe patient's acetabular cup relative to the bone axis line; f) usingdata associated with the inner surface of the three dimensional model ofthe patient's acetabular cup to manufacture the custom acetabular cuppositioning guide.
 14. The method of claim 13, wherein the medicalimaging slices are generated from MRI slices or CT slices.
 15. Themethod of claim 14, wherein the landmarks identified on the boneboundaries in the medical imaging slices include a left teardrop and aright teardrop of a pelvis, a right anterior-superior ilium symphysis(“ASIS-R”), a left anterior-superior ilium symphysis (“ASIS-L”), and apubic symphysis.
 16. The method of claim 15, wherein the landmarks areidentified in a coronal image slice.
 17. The method of claim 15, whereinthe landmarks used in triangulation in the two dimensional imagesinclude the ASIS-R, the ASIS-L, and the pubic symphysis.
 18. The methodof claim 16, wherein identifying the hip axis line further comprisesidentifying a pelvic axis line in the two dimensional images thatextends through the left teardrop and the right teardrop of the pelvis.19. The method of claim 18, further comprising determining an acutefirst angle between the pelvic axis line and a first line that extendsthrough the pubic symphysis and either the ASIS-R or ASIS-L, wherein thefirst line will extend through the ASIS-R if a right hip region is toundergo the arthroplasty procedure and the first line will extendthrough the ASIS-L if a left hip region is to undergo the arthroplastyprocedure.
 20. The method of claim 19, further comprising identifying asecond angle by increasing the first angle by a surgically prescribeddegree, rotated downward from the first line, wherein the second angleis coextensive with a hip axis angle, whereby the hip axis angle isdefined between the first line and the hip axis line.
 21. The method ofclaim 20, wherein the surgically prescribed degree is about forty-fivedegrees.